Ophthalmic lenses, such as contact lenses, made from polymeric materials, can be formed in molds comprising pairs of mold halves, i.e. a female mold half and a complementary male mold half. Typically, the polymerizable material is inserted into the female mold half and the male mold half is then brought together with the female mold half, producing a closed, filled mold assembly. In commercial scale ophthalmic lens production methods, a plurality of filled mold assemblies can be produced, such that a plurality of lenses can be formed simultaneously. In known methods and apparatus for bringing together the mold halves and forming a closed filled mold assembly, the position of the mold halves relative to one another is what is commonly used in order to verify that the two mold halves are acceptably closed. The relative position of the mold halves can, for example, be determined by sensing the distance between the mold halves or by bringing the mold halves to predetermined positions relative to each other, where the predetermined positions have previously been determined to correspond to positions where the mold assembly is known to be fully closed.
A rapid mold closure method is needed to support high-throughput manufacturing lines. It has been found, however, that if two mold halves are brought together at a too rapid velocity, imperfections can frequently occur in the final lens cast molded in the molds. For example, when the convex mold surface of a male mold half impacts a polymerizable composition present in the concave mold surface of a female mold half and the impact occurs too quickly, splashing of the polymerizable composition can occur, bubbles can be introduced into the lens-shaped cavity, and bubbles can be introduced to the polymerizable composition. Often, these bubbles will remain during the curing process, creating a bubble defect or a void in the lens body. This is particularly problematic with polymerizable compositions for forming silicone hydrogel contact lenses because they have been found to have a particular tendency to form bubbles when impacted. It has been found, however, that when the mold halves are moved and brought into contact with each other at too slow a velocity, the polymerizable composition can spread outwards on the male mold half, resulting in an inadequate volume of polymerizable composition remaining in the female mold half. The inadequate volume can cause a void and hence an incomplete lens to be formed. Closing the mold halves slowly is also in conflict with the desirability of completing the closure process as rapidly as possible.